Luminous tube



"Feb. 21, 1933. J BYRNES 1,898,615

LUMINOUS TUBE Filed Aug. 13. 1928 FIE l INVENTOR Jame: h. figr/v zs A TTORNE Y5 Patented Feb. 21, 1933 l.898,tli

UNITED STATES PATENT, OFFICE JAMES H. BYRNES, OF SAN FRANCISCO, CALIFORNIA ASSIGN OR T0 ELECTRON LIGHTS,

I INC., OF SAN 'JPIRAIQ'GISCO, CALIFORNIA, Ad CORPORATION OF CALIFORNIA LUMINOUS TUBE Application filed August 18, 1928. Serial No. 299,288.

This invention relates to luminous or inert gaseous discharge tubes, some forms of which are now in common use for advertising and display purposes.

The successful operation of such tubes present numerous diiliculties. For example, the intensity of light emitted is proportional to the current used. But since the heat developed is proportional to the square of the current passing thru the tube and since the vaporization of the electrodes is proportional to the heat developed, the intensity of light is limited unless, some means is provided for oped at the cathode. Needless to say, vaporization of the electrodes is detrimental for various reasons; the pressure within the tube is changed, the metallic vapor is likelyto beionized, a metallic deposit iscondensed on the walls of the tubing impairing its transparency and there is a disintegration of the electrodes. p

And since for advertising purposes tubes of this nature are exposed to atmospheric conditions it is essential'thatl they be oper-' ated at substantially atmospheric tempera tures in order to prevent breakage. It is also conceivable that for reasons other than that above stated, itvmight be desirable to pass relatively heavy currents'thru these tubes.

. Sputtering of the cathode'is another phenomenon that. is detrimental to the opera-.

' tion of the;tube inasmuch as the metallic particles thrown off from the cathode and deposited on the walls of the tubing eventually occlude or entrap sufficient quantities of the gas used as a working medium to decrease its pressure below its critical pressureof operation. Unlike vaporization, sputtering is attributed to the electrical condition prevailing on the surface of the cathode rather than to any heat efiects. It has been found that sputtering takes place in a direction normal to the electrode surface. i Another'dificulty encountered in the suc- '\cessful operation of gaseous discharge tubes is the eliminationof the presence of foreign gases within the working medium used (inert gases such as neon, argon, helium. etc.)

for thevery slightest trace ofa foreign gas may wholly alter, or entirely obliterate the visible spectrum of the rare gas. Great care must therefore be taken in purifying-the working medium to be used'and in driving 011' the foreign gases occluded in both the electroges and in the walls of the glass tubing use In general it is the object of this invention to providea luminous tube provided with means for continually purifying the working medium used during the operation of the tube and having a cathode capable of being cooled and so constructed'as to materially decrease the detrimental efi'ects of sputtering.

The invention possesses other advantageous features, some of which with the foregoing will be set forth at length in the fol-- lowing description where I shall outline in full that form of my invention, which I have selected for illustration in the drawing accompanying and forming part of the present specification. In said drawing I have shown one form of my invention, but it is to be understood that I do not limit 'myself to such form since the invention, as set forth in the claims, may be embodied in a plurality of forms.

Referring to the drawing:

Fig. 1 is a plan view of a luminous tube fication shown, the tubing has been bent upon itself anuniber of times in order to form a plurality of spaced coils as clearly shown in Figs. 1, 2 and 3. This particular construction produces a concentrated light which has been found to be very desirable for use as beacons or pilot lights The spaces between adjacent coils serve to insu- Fig. 4 is a vertical section of a modified'-* sure below late them from each other thereby preventing a breaking down of the walls of the tubing when it '15 beingwoperated at high potentials.

The cathode end 2 of the glass tubing 1 is outwardly. flared and is sealed to a cylindrical copper electrode 3. The. outer end of the electrode 3 is closed by means of conical walls 4. Since, as above stated, sputtering occurs normal to the surfaces of emission, it will be noted that sputtering from the end walls a of the electrode 3 result in the "deposition of the particles so sputtered on the cylindrical walls. of an electrode 3. Sputtering from the cylindrical walls of the electrode results in a deposition of the particles on the cylindrical walls diametrically opposite the surface of emission. This construction therefore substantially prevents any deposition of sputtered particles on the walls of the glass tubing per se. As is well recognized, the deposition of sputtered particles on the walls of either or both of the electrode and glass tubing results, in the occlusion or entrapment of suflicient amounts of the working medium used to decrease its presits critical value. However,

' molecules of the working medium entrapped by the deposition of sputtered particles are released by re-sputtering. It will therefore be seen that as long as the form of electrode used is such as to permit re-sputtering, a condition of equilibrium will eventually be reached whereby the amount of working me-- dium being occluded or entrapped due to sputtering is exactly equal to the amount of working medium being liberated by re-sputtering. Sputtering and re-sputtering is only possible from the electrode surface itself or from a metallic continuation thereof. This is possibly,explicable on the theory that sputtering isnot aconsequenceof heat, but rather a result of the electrical condition existing on the electrode surfaces. At all events, sputtering or re-sputtering from a metallic deposition on the walls of the glass tubing and insulated by portions of the glass tubing from the electrode, cannot take place. It will therefore be seen that in order to maintain the pressure of the working medium above its critical value it is advantageous to confine all depositions due to sputtering to;

branch 13 of the trap sealed by a teat 14.v

Since the ionization potentials of the vapors of chemical getters usually used in cleansing gaseous discharge tubes prior to placing them in operation, are below the ionization potentials of the inert gases used as a working medium, the vaporization of the chemical getters within the trap 7 would be fatal to the proper operation of the tube. However, the degree of heat necessary for efiecting the vaporization of the getter within the trap 7 is never attained for the trap 7 is placed at some distance from the electrodes and since it is not in the direct path of the ionized working medium, it cannot be subjected to a bombardment thereby. The nipple 9 precludes the possibility of the getter 12 in its solid state from entering the tubing 1. A continuous purification of the working medium used is efiected by the getter. 12 due to the fact that this getter either absorbs or combines with such impurities during the actual operation of the tube. Following Daltons law of partial pressures, the pressure of the working medium is not reduced below its critical pressure by such a reaction, for in a mixture of gases each gas exerts the same pressure as it would exert if it were alone present in the volume occupied by the mixture.

The difficulties customarily encountered in operating the usual form of gaseous discharge tube have in a measure been diminished in the luminous tube as above described. Since a substantial portion of the external surface of the electrodes 3 may be'placed in contact with the atmosphere or other suitable cooling fluid, the heat generated by the current passing thru these electrodes, may be quickly radiated or conveyed away, thereby cooling the electrodes and preventing undue vaporization. fins may be provided on the electrodes. This permits of the use of far greater current densities than otherwise possible, and since If desirable cooling the intensityof the light produced is-proportional to the current density, the intensity of the'light produced may be greatly increased. The particular form of the closed end of the electrodes confines the deposition of the small particles of the electrodes caused by sputtering,.to the surfaces of the electrodes or to a continuation thereof. This, as above explained, decreases the detrimental effects of sputtering. The provision of a continuously operating getter trap obviates the necessity of driving ofi the gasestoccluded in the electrodes and the walls of the glass tubing prior to placing it in operation, and since the driving off of gases so occluded materially increases the cost of production, the

convenient form'and like the cathode, may

be cooled in any suitable manner.

It will be found that if on long continued use the sodium, potassium or other purifying agent used in the trap 7 becomes coated due to its combination with the impure gases inthe tube, it may be readily resurfaced by a slight application of heat. In doing this there is no danger of sodium, potassium or other vapors passing into the main tubing line for what vapors are formed are quickly recondensed on cooler portions of the trap before they have a chance to pass out thru the nipple 9. This resurfacing process is of course carried out while the tube is out of use and may conveniently be done by a match flame.

I claim:

1. A luminous tube of the character de scribed sealed at one end with a hollow tubular cathode having a closed conical end, said cathode having a substantial portion of its surface external to said tube.

2. A luminous gaseous discharge tube of the character described comprisng a tubular glass wall open at its opposite ends, metal I thimble-like electrodes secured to and seal ing the ends of the tube with their open ends facing opposite the open ends of the tube and the extreme end of at least one of'said electrodes being of conical form interiorly.

3. A luminous gaseous discharge tube of the character described comprising a tubular glass wall open at its opposite ends, metal thimble-like electrodes secured to and sealing the ends of the tubewith their open ends facing opposite the open ends of the tube and forming substantially a continuation of Its walls and the extreme end of at least one of said electrodes being of conical form inthe sides of the tube in such a manner that substantially all lines extending perpendicularly from the inner surface of said wall will impinge against the inside of said electrode.

6. A luminous gaseous discharge tube of the character described comprising an elongated glass tube provided with electrodes at opposite ends, and a trap extending outwardly from the side of said tube at a point intermediate of and relatively remote from the electrodes, said trap containing a quantity of an alkali metal and provided with a restricted orifice communicating with the interior of the tube.

7. A luminous gaseous discharge tube of the character described comprisng an elongated glass tube provided with electrodes at opposite ends, and a trap extending outwardly from the side of said tube at a point intermediate of and relatively remote from the electrodes, said trap containing a gas absorbing material and provided with a neck extending substantially within its interior pierced by a restricted orifice communicating withthe interior of the tube.

my hand.

JAMES H. BYRNES.

of the character described a glass tube pro vided with a thimble-like metal electrode sealing the end of the tube, said electrode being a comparatively deep hollow cylinder extending beyond the tube with its outer end closed by a wall arranged at an angle with 

